New Materials and Advanced Applications in Photocatalysis

The development of visible-light-responsive (VLR) semiconductor materials for effective water oxidation is significant for a sustainable and better future. Among various candidates, bismuth tungstate (Bi₂WO₆; BWO) has attracted extensive attention because of many advantages, including efficient light-absorption ability, appropriate redox properties (for O₂ generation), adjustable morphology, low cost, and profitable chemical and optical characteristics. Accordingly, a facile solvothermal method has been proposed in this study to synthesize two-dimensional (2D) BWO nanoplates after considering the optimal preparation conditions (solvothermal reaction time: 10–40 h). To find the key factors of photocatalytic performance, various methods and techniques were used for samples’ characterization, including XRD, FE-SEM, STEM, TEM, HRTEM, BET-specific surface area measurements, UV/vis DRS, and PL spectroscopy, and photocatalytic activity was examined for water oxidation under UV and/or visible-light (vis) irradiation. Famous commercial photocatalyst–P25 was used as a reference sample. It was found that BWO crystals grew anisotropically along the {001} basal plane to form nanoplates, and all properties were controlled simultaneously by tuning the synthesis time. Interestingly, the most active sample (under both UV and vis), prepared during the 30 h solvothermal reaction at 433 K (BWO–30), was characterized by the smallest specific surface area and the largest crystals. Accordingly, it is proposed that improved crystallinity (which hindered charge carriers’ recombination, as confirmed by PL), efficient photoabsorption (using the smallest bandgap), and 2D mesoporous structure are responsible for the best photocatalytic performance of the BWO–30 sample. This report shows for the first time that 2D mesoporous BWO nanoplates might be successfully prepared through a facile template-free solvothermal approach. All the above-mentioned advantages suggest that nanostructured BWO is a prospective candidate for photocatalytic applications under natural solar irradiation. Full article

In this study, we proposed photocatalysts based on graphite-like carbon nitride with a low content (0.01–0.5 wt.%) of noble metals (Pd, Rh) for hydrogen evolution under visible light irradiation. As precursors of rhodium and palladium, labile aqua and nitrato complexes [Rh₂(H₂O)₈(μ-OH)₂](NO₃)₄∙4H₂O and (Et₄N)₂[Pd(NO₃)₄], respectively, were proposed. To obtain metallic particles, reduction was carried out in H₂ at 400 °C. The synthesized photocatalysts were studied using X-ray diffraction, X-ray photoelectron spectroscopy, UV–Vis diffuse reflectance spectroscopy and high-resolution transmission electron microscopy. The activity of the photocatalysts was tested in the hydrogen evolution from aqueous and aqueous alkaline solutions of TEOA under visible light with a wavelength of 428 nm. It was shown that the activity for the 0.01–0.5% Rh/g-C₃N₄ series is higher than in the case of the 0.01–0.5% Pd/g-C₃N₄ photocatalysts. The 0.5% Rh/g-C₃N₄ sample showed the highest activity per gram of catalyst, equal to 3.9 mmol g_cat^–1 h^–1, whereas the most efficient use of the metal particles was found over the 0.1% Rh/g-C₃N₄ photocatalyst, with the activity of 2.4 mol per gram of Rh per hour. The data obtained are of interest and can serve for further research in the field of photocatalytic hydrogen evolution using noble metals as cocatalysts. Full article

Photocatalysts with located surface plasmon resonance effects (LSPRs) have been studied in recent years due to their superior light harvesting capacity and photocatalytic performance in solving environmental problems and energy shortages. Plasmonic-noble-based photocatalysts are limited in terms of their practical application on account of their high cost, fixed plasma frequency, and low abundance. In order to solve these shortcomings, non-noble metal and nonmetallic plasmonic photocatalysts with LSPRs and advantages such as a lower cost and wider light adsorption range from the UV to NIR region have been developed. This paper reviews the recent development of non-noble metal and nonmetallic plasmonic photocatalysts and advances the research direction of plasmonic photocatalysts to achieve high photocatalytic activity and stability, providing guidance for photocatalysis to solve environmental problems and energy shortages. Full article

As one of the widely studied semiconductor materials, titanium dioxide (TiO₂) exhibits high photoelectrochemical (PEC) water-splitting performance as well as high chemical and photo stability. However, limited by a wide band gap and fast electron-hole recombination rate, the low solar-to-hydrogen conversion efficiency remains a bottleneck for the practical application of TiO₂-based photoelectrodes. To improve the charge separation and water oxidation efficiency of TiO₂ photoanodes, antimonene, a two-dimensional (2D) material obtained by liquid-phase exfoliation, was assembled onto TiO₂ nanorod arrays (TNRAs) by a simple drop-coating assembly process. PEC measurements showed that the resulting 2D Sb/TiO₂ photoelectrode displayed an enhanced photocurrent density of about 1.32 mA cm⁻² in 1.0 M KOH at 0.3 V vs. Hg/HgO, which is ~1.65 times higher than that of the pristine TNRAs. Through UV-Vis absorption and electrochemical impedance spectroscopy measurements, it was possible to ascribe the enhanced PEC performances of the 2D Sb/TiO₂ photoanode to increased absorption intensity in the visible light region, and improved interfacial charge-transfer kinetics in the 2D Sb/TiO₂ heterojunction, which promotes electron-hole separation, transfer, and collection. Full article

In this article, we reported a novel setup treatment using nitric acid vapor to treat g-C₃N₄ (CN). By treatment with nitric acid vapour, the basic structure of the CN has not been destroyed. These adoptive treatments enhanced the photocatalytic performance of CN and were reflected in the elimination of rhodamine B (RhB) as well as tetracycline hydrochloride (TC). In comparison to CN, CN-6 demonstrated the highest photocatalytic yield for the breakdown of RhB (99%, in 20 min). Moreover, the excellent reuse of CN-6 for breaking down RhB was also demonstrated. This clearly demonstrated that treatment with nitric acid vapor promoted a blue shift, positively extended its valence band position, and increased the oxidizability of the holes. This also caused CN to disperse better into the aqueous phase, introducing more oxygen-containing functional groups. Thus, treatment with nitric acid vapor has the potential to be applied to delaminate the CN in order to enhance photocatalytic activity. Full article

In this work, we report the effect of zinc (Zn) and nickel (Ni) co-doping of hydrothermally synthesized hematite nanorods prepared on fluorine-doped tin oxide (FTO) substrates for enhanced photoelectrochemical (PEC) water splitting. Seeded hematite nanorods (NRs) were facilely doped with a fixed concentration of 3 mM Zn and varied concentrations of 0, 3, 5, 7, and 9 mM Ni. The samples were observed to have a largely uniform morphology of vertically aligned NRs with slight inclinations. The samples showed high photon absorption within the visible spectrum due to their bandgaps, which ranged between 1.9–2.2 eV. The highest photocurrent density of 0.072 mA/cm² at 1.5 V vs. a reversible hydrogen electrode (RHE) was realized for the 3 mM Zn/7 mM Ni NRs sample. This photocurrent was 279% higher compared to the value observed for pristine hematite NRs. The Mott–Schottky results reveal an increase in donor density values with increasing Ni dopant concentration. The 3 mM Zn/7 mM Ni NRs sample produced the highest donor concentration of 2.89 × 10¹⁹ (cm⁻³), which was 2.1 times higher than that of pristine hematite. This work demonstrates the role of Zn and Ni co-dopants in enhancing the photocatalytic water oxidation of hematite nanorods for the generation of hydrogen. Full article

Graphene-TiO₂ composites have been investigated in various photocatalytic reactions showing successful synergy compared to pristine TiO₂. In the present work, graphene oxide (GO) was synthesized by the Hummers method and then reduced graphene oxide-TiO₂ composites (rGO/TiO₂) were obtained by an in situ GO photoreduction route. X-ray diffraction, FTIR, Raman, UV–vis DRS, and photoluminescence were the main characterization techniques. The obtained composites containing 1 and 3 wt.% rGO were evaluated in the cyanide (50 mg/L) oxidation and Au-cyanide complex (300 mg/L) degradation under UV-A light. The composites showed higher photocatalytic activity than TiO₂, mainly with the 1% rGO content. Cyanate and gold nanoparticles, deposited on the photocatalyst’s surface, were the main byproducts during the photocatalyst assessment. The improved photocatalytic activity of the composites was attributed to a higher rate of electron transfer and a lower rate of charge recombination due to the chemical interaction of rGO with TiO₂. Full article

The persistence of pharmaceuticals and personal care products (PPCPs) in water has been a cause for concern for several years. Many studies have successfully used TiO₂/UV photocatalysis to remove these compounds from water. In order to optimize these systems for large-scale water treatment, the effects of the reaction matrix, methods to improve energy efficiency, and methods for easy catalyst separation must be considered. The following study examines the photocatalytic degradation of a cocktail of 18 PPCPs using a porous titanium–titanium dioxide membrane and the effect of solution pH on kinetic rate constants. The addition of methanol to the reaction—commonly used as a carrier solvent—had a significant effect on kinetic rate constants even at low concentrations. Solution pH was also found to influence kinetic rate constants. Compounds had higher kinetic rate constants when they were oppositely charged to the membrane at experimental pH as opposed to similarly charged, suggesting that electrostatic forces have a significant effect. The controlled periodic illumination of UV–LEDs was also investigated to increase photonic efficiency. The dual-frequency light cycle used did not cause a decrease in degradation for many compounds, successfully increasing the photonic efficiency without sacrificing performance. Full article

In this study, expired egg white was used as a template, and a sol–gel method was employed to prepare pure-phase TiO₂ nano-powder and mixed-phase powders doped with NaF and NaI. The influences of different calcination temperatures, doping elements, and doping amounts during the preparation process on the photocatalytic performance and activity of the prepared TiO₂ powders were studied. The results of the experiments showed that the F-doped TiO₂ had the highest photocatalytic activity when the doping amount was 1.2%, as examined by EDS, where the sintering temperature was 500 °C. F-doped TiO₂ nanoparticles were also synthesized by the sol–gel method using tetrabutyl titanate and NaF mixed with expired egg white protein as the precursor. The F-TiO₂ photocatalyst was characterized using FE-SEM, HR-TEM, EDS, XPS, and UV-Vis, and the photocatalytic activity was evaluated by photodegradation of methylene blue under visible light. The results showed that doping with F reduced the energy band gap (3.04 eV) of TiO₂, thereby increasing the photocatalytic activity in the visible-light region. The visible-light wavelength range and photocatalytic activity of the catalyst were also affected by the doping amount. Full article

In this study, TiO₂-based photocatalysts modified with Pt and Cu/CuO_x were synthesized and studied in the photocatalytic reduction of CO₂. The morphology and chemical states of synthesized photocatalysts were studied using UV-Vis diffuse reflectance spectroscopy, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. A series of light-emitting diodes (LEDs) with maximum intensity in the range of 365–450 nm was used to determine the action spectrum of photocatalysts. It is shown for, the first time, that the pre-calcination of TiO₂ at 700 °C and the use of Cu/CuO_x instead of Pt allow one to design a highly efficient photocatalyst for CO₂ transformation shifting the working range to the visible light (425 nm). Cu/CuO_x/TiO₂ (calcined at 700 °C) shows a rate of CH₄ formation of 1.2 ± 0.1 µmol h⁻¹ g⁻¹ and an overall CO₂ reduction rate of 11 ± 1 µmol h⁻¹ g⁻¹ (at 425 nm). Full article

Photocatalytic hydrogen evolution is considered one of the promising routes to solve the energy and environmental crises. However, developing efficient and low-cost photocatalysts remains an unsolved challenge. In this work, ultrathin 2D g-C₃N₄ nanosheets are coupled with flat TiO₂ nanoparticles as face-to-face 2D/2D heterojunction photocatalysts through a simple electrostatic self-assembly method. Compared with g-C₃N₄ and pure TiO₂ nanosheets, 2D/2D TiO₂/g-C₃N₄ heterojunctions exhibit effective charge separation and transport properties that translate into outstanding photocatalytic performances. With the optimized heterostructure composition, stable hydrogen evolution activities are threefold and fourfold higher than those of pure TiO_2, and g-C₃N₄ are consistently obtained. Benefiting from the favorable 2D/2D heterojunction structure, the TiO₂/g-C₃N₄ photocatalyst yields H₂ evolution rates up to 3875 μmol·g⁻¹·h⁻¹ with an AQE of 7.16% at 380 nm. Full article